A fuel cell that is a main power supply source of a fuel cell system is a device that produces electricity while producing water by receiving hydrogen, which is a fuel, and oxygen, which is an oxidizing agent. High purity hydrogen is supplied from a hydrogen storage tank to an anode (fuel electrode) of a fuel cell stack, and air in the atmosphere containing, e.g., oxygen, is directly supplied to a cathode (air electrode) of the fuel cell stack by an air supply device such as an air compressor.
Hydrogen supplied to the anode is split into hydrogen ions (protons) and electrons by a catalyst of the anode, and the protons are conducted through a polymer electrolyte membrane to the cathode. Oxygen in the air supplied to the cathode is combined with the electrons which have traveled to the cathode through an external circuit to form water and generate electrical energy.
As the polymer electrolyte membrane is sufficiently wet with moisture, ion conductivity increases and loss due to resistance decreases. In addition, when the supply of a reactant gas having a low relative humidity continues, the polymer electrolyte membrane becomes dry and may no longer be used. Therefore, humidification of the reactant gas is essential in the fuel cell system, and thus the fuel cell system may generally be provided with a humidifier capable of humidifying the reactant gas.
Meanwhile, the reactant gas humidified by the humidifier may be supplied to the fuel cell stack through a gas supply line. In the gas supply line, moisture contained in the reactant gas may be condensed due to low ambient temperature, to form condensed water. In addition, the condensed water generated during the humidification of the reactant gas in the humidifier may flow into the gas supply line together with the reactant gas. The condensed water may flow, together with the reactant gas, into the interior of the fuel cell stack, and then flow into fuel cells. Most of the condensed water flowing into the interior of the fuel cell stack may flow intensively into a fuel cell located at an inlet side of the fuel cell stack. In the inlet side fuel cell of the fuel cell stack, continuous presence of excessive condensed water may frequently cause degradation of the anode and the cathode (hereinafter referred to as the “electrodes”). The degradation of the electrodes is a key factor in decreasing the durability of the fuel cell system.
Therefore, a conventional fuel cell stack includes a dummy cell disposed between the inlet side fuel cell and an end plate in order to prevent the degradation of the electrodes. The dummy cell includes a gas supply manifold guiding the reactant gas supplied from the outside of the fuel cell stack to the fuel cells, a gas exhaust manifold guiding the reactant gas having passed through the fuel cells to the outside, and a bypass channel connecting the gas supply manifold to the gas exhaust manifold to guide the condensed water passing through the gas supply manifold to the gas exhaust manifold. Due to the presence of the dummy cell, the condensed water introduced into the interior of the fuel cell stack fails to enter the fuel cells, and is discharged to the outside of the fuel cell stack through the bypass channel of the dummy cell. However, not only the condensed water but also part of the reactant gas introduced into the interior of the fuel cell stack may be forced to flow into the bypass channel.
Therefore, in the conventional fuel cell stack, part of the reactant gas may be discharged to the outside of the fuel cell stack through the bypass channel without reaching the fuel cells, and thus the efficiency of the fuel cell system may be lowered.